Yield of excited CO molecules from dissociative recombination of HCO+ and HOC+ ions with electrons

The authors have investigated CO band emissions arising from the dissociative recombination of HCO(+) and HOC(+) ions with thermal electrons in a flowing afterglow plasma. The quantitative analysis of the band intensities showed that HCO(+) recombination forms the long-lived CO(a (3)Pi) state with a yield of 0.23+/-0.12, while HOC(+) recombination favors formation of CO(a' (3)Sigma(+)) and CO(d (3)Delta) with a combined yield of greater than 0.4. The observed vibrational distribution for the CO(a) state reproduces theoretical predictions quite well. The vibrational distributions for CO(a') and CO(d) are, in part, inverted, presumably as a consequence of a change in CO equilibrium bond length during recombination. The observations are compatible with current knowledge of the potential surfaces of states of HCO and HCO(+).     

Ab initio rotation-vibration spectra of HCN and HNC

We have calculated an ab initio HCN/HNC linelist for all transitions up to J= 25 and 18000 cm(-1) above the zero point energy. This linelist contains more than 200 million lines each with frequencies and transition dipoles. The linelist has been calculated using our semi-global HCN/HNC VQZANO + PES and dipole moment surface, which were reported in van Mourik et al. (J. Chem. Phys. 115 (2001) 3706). With this linelist we synthesise absorption spectra of HCN and HNC at 298 K and we present the band centre and band transition dipoles for the bands which are major features in these spectra. Several of the HCN bands and many of the HNC bands have not been previously studied. Our line intensities reproduce via fully ab initio methods the unusual intensity structure of the HCN CN stretch fundamental (00(0)1) for the first time and also the forbidden (02(2)0) HCN bending overtone. We also compare the J = 1-->0 pure rotational transition dipole in the HCN/HNC ground and vibrationally excited states with experimental and existing ab initio results.     

In situ generation of HCN for mass spectrometric studies

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me(3)SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F(-)(HCN), Cl(-)(HCN), CN(-)(HCN), PhNO(2)(.-)(HCN), Me(3)SiO(-)(HCN),and PhSiF(4)(-)(HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN(-)(HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0.87 +/- 0.07 eV.     

Experimental and theoretical studies of the CN-Ar van der Waals complex

The CN-Ar van der Waals complex has been observed using the B (2)Sigma(+)-X (2)Sigma(+) and A (2)Pi-X (2)Sigma(+) electronic transitions. The spectra yield a dissociation energy of D(0")=102+/-2 cm(-1) and a zero-point rotational constant of B(0")=0.067+/-0.005 cm(-1) for CN(X)-Ar. The dissociation energy for CN(A)-Ar was found to be D(0')=125+/-2 cm(-1). Transitions to vibrationally excited levels of CN(B)-Ar dominated the B-X spectrum, indicative of substantial differences in the intermolecular potential energy surfaces (PESs) for the X and B states. Ab initio PESs were calculated for the X and B states. These were used to predict rovibrational energy levels and van der Waals bond energies (D(0")=115 and D(0')=183 cm(-1)). The results for the X state were in reasonably good agreement with the experimental data. Spectral simulations based on the ab initio potentials yielded qualitative insights concerning the B-X spectrum, but the level of agreement was not sufficient to permit vibronic assignment. Electronic predissociation was observed for both CN(A)-Ar and CN(B)-Ar. The process leading to the production of CN(A,nu=8,9) fragments from the predissociation of CN(B,nu=0)-Ar was characterized using time-resolved fluorescence and optical-optical double resonance measurements.     

NO reburning study based on species quantification obtained by coupling LIF and cavity ring-down spectroscopy

NO reburning is studied in a low pressure (15 hPa) premixed flame of CH4-O2 seeded with 1.8% of NO. Measurements were carried out by using cavity ring-down spectroscopy (CRDS) and laser induced fluorescence (LIF) techniques. The temperature profile was obtained by OH-LIF thermometry in the A-X (0-0) band. The OH profile was determined by LIF and calibrated by single pass absorption. The NO concentration profile was obtained by LIF in the A-X (0-0) band and corrected for Boltzmann fraction and quantum yield variations. The absolute concentration profile was determined in the burned gases by CRDS allowing a direct experimental determination of the NO reburning amount. Finally CH and CN mole fraction profiles were obtained by CRDS by exciting rotational transitions in the B-X (0-0) bands of CH and CN around 387 nm. We found a peak mole fraction of 29 ppm for CH and 3.3 ppm for CN. This last result is in contrast with a previous study of W. Juchmann, H. Latzel, D. L. Shin, G. Peiter, T. Dreier, H. R. Volpp, J. Wolfrum, R. P. Lindstedt and K. M. Leung, XXVIIth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, 1998, p. 469, performed in a similar flame, which reported much lower levels of CN. In that study the absolute concentration of CN was indirectly obtained by LIF calibrated by Rayleigh scattering. In a second part, experimental species profiles are compared with predictions of the GRI 3.0 mechanism. Comparison between experimental and predicted profiles shows a good agreement particularly for CN and NO species. A qualitative analysis of NO reburning is then performed.     

Electronic spectroscopy of the previously unknown arsenic carbide (AsC) free radical

The previously unknown arsenic carbide (AsC) free radical has been identified in the gas phase through a combination of laser-induced fluorescence (LIF), single vibronic level emission, and stimulated emission pumping (SEP) spectroscopy in a supersonic expansion. The As(12)C and As(13)C isotopologues have been detected as products of an electric discharge in mixtures of arsine (AsH(3)) and carbon dioxide ((12)CO(2) or (13)CO(2)) in high pressure argon. The B (2)Σ(+)-X (2)Σ(+) band system was recorded by LIF spectroscopy and emission transitions from the B state down to the ground state and to the low-lying A (2)Π(i) state were observed. High resolution studies of the B-X 0-0 band by LIF and the B-A 0-0 band by SEP spectroscopy enabled a determination of the molecular structures in the three states. Although CN, CP, and AsC have similar X (2)Σ(+) and A (2)Π(i) states, the B (2)Σ(+) state molecular orbital configuration of CP and AsC differs from that of the CN free radical.     

Kinetics of the NCO + HCNO reaction

The kinetics of the NCO + HCNO reaction were studied using infrared diode laser absorption spectroscopy. The total rate constant was measured to be k(1) = (1.58 +/- 0.20) x 10(-11) cm(3) molecule(-1) s(-1) at 298 K. After detection of products and consideration of secondary chemistry (primarily O + HCNO and CN + HCNO), we conclude that NO + CO + HCN is the major product channel (phi = 0.92 +/- 0.04), with a minor contribution (phi = 0.04 +/- 0.02) from CO2 + HCNN.     

烯丙基自由基(·C3H5)与一氧化氮(NO)反应势能面的理论研究

在CCSD(T)/6-311G(d,p)//B3LYP/6-311G(d,p)+ZPE水平上对反应·CHCHCH3+NO进行了计算, 并建立了其单重态的反应势能面. 在该反应中, 分别找到生成P1(CH3CHO+HCN), P2(CH3CHO+HNC), P3(CH3CN+HCHO), P4(CH3CCH+HNO)的4条产物通道, 其中·CHCHCH3和NO中的氮原子直接连接形成m1(trans-CH3CHCHNO), m1经过顺反异构形成m2(cis-CH3CHCHNO), m2再经过CCNO四元环合, 然后发生环解离, 最后生成产物P1(CH3CHO+HCN)是最可行的产物通道, 其余三条通道为次要产物通道. 该体系中生成P1的反应路径与同类体系·C2H3+NO的主要反应路径相类似, 两者的差别是前者为动力学可行的反应, 而后者为动力学不可行反应, 这使得·CHCHCH3+NO反应比·C2H3+NO反应更具有实际意义.     

Gas-phase photodissociation of CH3COCN at 308 nm by time-resolved Fourier-transform infrared emission spectroscopy

By using time-resolved Fourier-transform infrared emission spectroscopy, the fragments of HCN(v = 1, 2) and CO(v = 1-3) are detected in one-photon dissociation of acetyl cyanide (CH(3)COCN) at 308 nm. The S(1)(A(")), (1)(n(O), π(?) (CO)) state at 308 nm has a radiative lifetime of 0.46 ± 0.01 μs, long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of Ar collision-induced internal conversion is estimated to be (1-7) × 10(-12) cm(3) molecule(-1) s(-1). The measurements of O(2) dependence exclude the production possibility of these fragments via intersystem crossing. The high-resolution spectra of HCN and CO are analyzed to determine the ro-vibrational energy deposition of 81 ± 7 and 32 ± 3 kJ∕mol, respectively. With the aid of ab initio calculations, a two-body dissociation on the energetic ground state is favored leading to HCN + CH(2)CO, in which the CH(2)CO moiety may further undergo secondary dissociation to release CO. The production of CO(2) in the reaction with O(2) confirms existence of CH(2) and a secondary reaction product of CO. The HNC fragment is identified but cannot be assigned, as restricted to a poor signal-to-noise ratio. Because of insufficient excitation energy at 308 nm, the CN and CH(3) fragments that dominate the dissociation products at 193 nm are not detected.     

Experimental and theoretical study of the electronic spectrum of the methylene amidogen radical (H2CN): verification of the 2A1 <-- 2B2 assignment

A collaborative experimental and theoretical study of the electronic spectrum and excited-state photochemistry of H(2)CN has been carried out. The absorption spectrum, in the range of 287-278 nm, was measured through cavity ring-down spectroscopy. The radical was prepared by 193 nm photolysis of monomeric formaldoxime vapor. Two diffuse features were observed in the 34800-35800 cm(-1) spectral range, along with the A-X (1,0) band of the OH cofragment. The broad features were assigned through high-level ab initio calculations as vibronic transitions to the ground and 2b(1) (umbrella mode) levels of the second excited B (2)A(1) state from the ground X (2)B(2) state of H(2)CN. Rotational constants for the lower and upper levels of these transitions were computed from the expectation values of the moments of inertia tensor, using the appropriate vibrational wave functions. Experimental and simulated rotational profiles of these bands agree extremely well with each other for an assumed type-B electric dipole-allowed (2)A(1) <-- (2)B(2) transition appropriate to this transition. The former assignment to the dipole-forbidden (2)B(1) <-- (2)B(2) transition can be ruled out by these results. A theoretical investigation of the dissociation pathways for electronically excited H(2)CN is also presented. The upper states of the observed bands cannot dissociate directly but rather decay through internal conversion and subsequent dissociation to H + HCN fragments; higher b(1) levels are above the excited-state dissociation limit.     

CO(α3П)与CN(X 2Σ +)的能量转移反应

Energy-transfer reaction from metastable CO(a~3П) molecule to CN radical has been studied in a room-temperature flow reactor. The CN (B-X, △v=0, ±1, ±2) violet emission bands were obtained. The △v=0 sequence of CN(B) were analyzed by computer simulation. The vibrational temperature is 3400 K. By using the reference reaction CO(a)+NO, the formation rate constant of CN(B) has been measured, k_(CN)(B)=1.1×10~(-11) cm~3·molecule~(-1)·s~(-1).     

Collisionally-induced dissociation of purine antiviral agents: mechanisms of ion formation using gas phase hydrogen/deuterium exchange and electrospray ionization tandem mass spectrometry

ESI and CID mass spectra were obtained for two purine nucleoside antiviral agents (acycloguanosine and vidarabine) and one purine nucleotide (vidarabine monophosphate) and the corresponding compounds in which the labile hydrogens were replaced by deuterium gas phase exchange. The number of labile hydrogens, x, was determined from a comparison of ESI spectra obtained with N(2) and with ND(3) as the nebulizer gas. CID mass spectra were obtained for [M+H](+) and [M -H](-) ions and the exchanged analogs, [M(Dx)+D](+) and [M(Dx)-D](-), produced by ESI using a Sciex API-IIIplus mass spectrometer. Compositions of product ions and mechanisms of decomposition were determined by comparison of the CID mass spectra of the undeuterated and deuterated species. Protonated purine antiviral agents dissociate through rearrangement decompositions of base-protonated [M+H](+) ions by cleavage of the glycosidic bonds to give the protonated bases with a sugar moiety as the neutral fragment. Cleavage of the same bonds with charge retention on the sugar moiety gives low abundance ions, due to the low proton affinity of the sugar moiety compared to that of purine base. CID of protonated purine bases [B+H](+) occurs through two major pathways: (1) elimination of NH(3) (ND(3)) and (2) loss of NH(2)CN (ND(2)CN). Minor pathways include elimination of HNCO (DNCO), loss of CO, and loss of HCN (DCN). Deprotonated acycloguanosine and vidarabine exhibit the deprotonated base [B-H](-) as a major fragment from glycosidic bond cleavage and charge delocalization on the base. Deprotonated vidarabine monophosphate, however, shows predominantly phosphate related product ions. CID of deprotonated guanine shows two principal pathways: (1) elimination of NH(3) (ND(3)) and (2) loss of NH(2)CN (ND(2)CN). Minor pathways include elimination of HNCO (DNCO), loss of CO, and loss of HCN (DCN). The dissociation reactions of deprotonated adenine, however, proceed by elimination of HCN and (2) elimination of NCHNH (NCHND). The mass spectra of the antiviral agents studied in this paper may be useful in predicting reaction pathways in other heteroaromatic ring decompositions of nucleosides and nucleotides.     

HNC/HCN ratio in acetonitrile, formamide, and BrCN discharge

Time-resolved Fourier transform (FT) spectrometry was used to study the dynamics of radical reactions forming the HCN and HNC isomers in pulsed glow discharges through vapors of BrCN, acetonitrile (CH(3)CN), and formamide (HCONH(2)). Stable gaseous products of discharge chemistry were analyzed by selected ion flow tube mass spectrometry (SIFT-MS). Ratios of concentrations of the HNC/HCN isomers obtained using known transition dipole moments of rovibrational cold bands v(1) were found to be in the range 2.2-3%. A kinetic model was used to assess the roles the radical chemistry and ion chemistry play in the formation of these two isomers. Exclusion of the radical reactions from the model resulted in a value of the HNC/HCN ratio 2 orders of magnitude lower than the experimental results, thus confirming their dominant role. The major process responsible for the formation of the HNC isomer is the reaction of the HCN isomer with the H atoms. The rate constant determined using the kinetic model from the present data for this reaction is 1.13 (±0.2) × 10(-13) cm(3) s(-1).     

Theoretical Study of Reaction Mechanism of 1-Propenyl Radical with NO

The reaction system of 1-propenyl radical with NO is an ideal model for studying the intermolecular and intramolecular reactions of complex organic free radicals containing C=C double bonds. On the basis of the full optimization of all species with the Gaussian 98 package at the B3LYP/6-311++G** level, the reaction mechanism was elucidated extensively using the vibrational mode analysis. There are seven reaction pathways and five sets of small molecule end products: CH2O+CH3CN, CH2CHCN+H2O, CH3CHO+HCN, CH3CHO+HNC, and CH3CCH+HNO. The channel of C3H5￠+NO→ IM1→TS1→IM2→TS2→IM3→TS3→CH3CHO+HCN is thermodynamically most favorable.     

Threshold ion-pair production spectroscopy of HCN

The spectroscopic technique of threshold ion-pair production spectroscopy (TIPPS) has been applied to the triatomic molecule HCN. We have recorded the total ion-pair yield and TIPP spectra for the HCN-->H(+) + CN(-) process using coherent vacuum ultraviolet excitation. From the simulation of our high-resolution TIPP spectrum we have precisely measured the HCN ion-pair threshold E(IP) (0) to be 122 244 +/- 4 cm(-1). This value could be used to determine the bond dissociation energy D(0)(H-CN) to unprecedented accuracy. Our fitting result also showed that rotationally excited instead of cold CN(-) fragment is favored as the ion-pair dissociation product in the threshold region.     

Theoretical study of HCN(+) + C2H2 reaction

A detailed theoretical investigation for the ion-molecule reaction of HCN (+) with C 2H 2 is performed at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels. Possible energetically allowed reaction pathways leading to various low-lying dissociation products are probed. It is shown that eight dissociation products P 1 (H 2C 3N (+)+H), P 2 (CN+C 2H 3 (+)), P 3 (HC 3N (+)+H 2), P 4 (HCCCNH (+)+H), P 5 (H 2NCCC (+)+H), P 6 (HCNCCH (+)+H), P 7 (C 2H 2 (+)+HCN), and P 8 (C 2H 2 (+)+HNC) are both thermodynamically and kinetically accessible. Among the eight dissociation products, P 1 is the most abundant product. P 7 and P 3 are the second and third feasible products but much less competitive than P 1 , followed by the almost negligible product P 2 . Other products, P 4 (HCCCNH (+)+H), P 5 (HCNCCH (+)+H), P 6 (H 2NCCC (+)+H), and P 8 (C 2H 2 (+)+HNC) may become feasible at high temperatures. Because the intermediates and transition states involved in the reaction HCN (+) + C 2H 2 are all lower than the reactant in energy, the title reaction is expected to be rapid, as is consistent with the measured large rate constant at room temperature. The present calculation results may provide a useful guide for understanding the mechanism of HCN (+) toward other pi-bonded molecules.     

Coordination and ligands’ effects in trinuclear [Pd3(COT)2(L)]2+ (L = H2O,CO, N2, HCN,HNC, NH3, PH3, PCl3, PF3, CS,CH2) sandwich complexes of cyclooctatetraene: theoretical investigation

Structural Chemistry - This paper reports the molecular structure, the electronic structure, and the decomposition energies of the [M3(COT)2(L)]2+ (M = Cr, Fe, Pd, and L = H2O, CO, N2, HCN, HNC,...     

Recombination of polycyclic aromatic hydrocarbon photoions with electrons in a flowing afterglow plasma

A new technique, flowing afterglow with photoions (FIAPI), has been developed to measure the rate coefficient for the recombination of complex ions, and, in particular, polycyclic aromatic hydrocarbon (PAH) cations with electrons. The method is based on the flowing afterglow Langmuir probe - mass spectrometer apparatus at the University of Rennes I. A helium plasma is generated by a microwave discharge in a He buffer gas and downstream, a small amount of argon gas is injected to destroy any helium metastables. A very small amount of neutral PAH molecules is added to the afterglow plasma by evaporation from a plate coated with the PAH to be studied. PAH ions are then produced by photoionization of the parent molecule using a pulsed UV laser (157 nm). The laser beam is oriented along the flow tube and so a constant spatial concentration of photoions is obtained. The electron concentration along the flow tube is measured by means of a movable Langmuir probe. Ion concentration decay in time is measured at a fixed position using a quadrupole mass spectrometer which is triggered by the laser pulse. The recombination of anthracene and pyrene cations has been studied using this technique and we have found a recombination rate of (2.4 +/- 0.8) x 10(-6) cm(3) s(-1) for anthracene and (4.1 +/- 1.2) x 10(-6) cm(3) s(-1) for pyrene.     

Ion-molecule reaction mechanism of SiCN+/SiNC+ + HX (X = H, CH3, F, OH, NH2)

In contrast to the abundant data on the neutral-neutral reactions, little is known about the ion-molecule reactions involving silicon ions. A detailed mechanistic study at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(2df,p) (single-point) computational levels was reported for the reactions of SiCN+/SiNC+ with a series of -bonded molecules HX (X = H, CH3, F, NH2). Together with the recently studied SiCN+/SiNC+ + H2O reactions, all of these reactions have nucleophilic substitution as their major pathway. Insertion is a much slower reaction. By contrast, the known atomic Si+ and C2N+ ion-molecule reactions go by insertion. Generally, the initial gas-phase condensation between SiCN+/SiNC+ and HX (except the nonionic H2) effectively forms the adduct HX...SiCN+/HX...SiNC+. The stability of the adduct increases with the electron-donating ability of X. Even at low temperatures, reactions with the electron donors NH3, H2O, and HF proceed rapidly to generate the fragments SiX+ + HCN (dominant) and SiX+ + HNC (minor). This suggests that such reactions may be useful in the synthesis of novel Si-X bonded species. However, the reactions of SiCN+ with completely saturated CH4 and H2 produce fragments only at high temperatures, and SiNC+ may even be unreactive. The calculated results may be helpful for understanding the chemistry of SiCN-based microelectric and photoelectric processes in addition to astrophysical processes in which the [Si,C,N]+ ion is involved. The results can also provide useful mechanistic information for the analogous ion-molecule reactions of the monovalent silicon-bearing ions.